1. Field of the Invention
The present invention relates to an image forming-process and, particularly, to an image forming process which has a photographic characteristic of providing a very contrasty negative image and which are suitable for reproduction of precise line drawings and an image forming process using the same.
2. Description of the Prior Art
A process which comprises adding hydrazine compounds to silver halide photographic emulsions to obtain a photographic characteristic of a contrasty negative image is described in U.S. Pat. No. 2,419,975. This patent discloses that a very contrasty photographic characteristic of a gamma (.gamma.) of more than 10 is obtained when hydrazine compounds are added to silver bromochloride emulsions and the emulsions are developed using a developing solution having a pH of as high as 12.8. However, a strongly alkaline developing solution having a pH near 13 is unstable because it is easily oxidized by air and, consequently, it cannot be stored or used for a long period of time. Further, silver bromochloride emulsions generally have a low sensitivity and are unsuitable for uses where a high sensitivity is required.
The supercontrasty photographic characteristic of a gamma of more than 10, for either a negative image or a positive image, is very useful for photographic reproduction of halftone images or reproduction of line drawing images by means of dot images useful for printing plates. In the past, for such a purpose, a process which comprises using silver bromochloride photographic emulsions having a silver chloride content of more than 50 mol% and preferably more than 75 mol% and developing such with a hydroquinone developing solution having a very low sulfite ion concentration (generally, less than about 0.1 mol/liter) has been used. However, in this process, the developing solution is very unstable because it has a low sulfite ion concentration and, consequently, the developing solution cannot be stored for 3 days or more. Further, since silver bromochloride emulsions having a comparatively high silver chloride content are used in this process, a high sensitivity cannot be obtained.
Accordingly, the ability to obtain a supercontrasty photographic characteristic useful for reproduction of dot images or line drawings using high speed emulsions and stable developing solutions has been very much desired.